All surveys accessed by the respondent, whether fully completed, partially completed or not completed at all, are stored in the database as units. In case a respondent has omitted a question, the missing value will be displayed for the variable in the database.
By default, the Data and Analyse tabs do not include empty or invalid units where there was no response to ANY question (e.g. the person just clicked on a link and left the survey after viewing the intro page). However, with an additional setting, units with invalid statuses can be included in the analysis.